The present invention relates to a developing agent used in an electrophotographic system or an electrostatic recording system, particularly, to a developing agent used in a two-part developing method in which is used a mixture of a toner and a carrier.
The dye mixed in a toner acts as a coloring material and, at the same, the electrostatic characteristics of the dye cause the dye to play an important role as a charge control agent. Particularly, the conventional dye is charged positive in many cases. Even if charged negative, the charging is weak. Therefore, in the case of using a conventional negatively charged toner, difficulties such as fogging are generated, resulting in failure to obtain a clear image.
The negatively charged dye includes a 2:1 type metal complex salt dye disclosed in, for example, Japanese Patent Disclosure (KOKOKU) No. 2-16916. However, the 2:1 type metal complex salt dye is poor in charging properties such as rising and in charging stability in the case of applying a life, resulting in failure to obtain a satisfactory image.
Further, the conventional dyes, which are essentially low in the negative charging performance, are poor in compatibility with a binder resin. As a result, these dyes are not dispersed uniformly in toner particles, making it quite impossible to obtain a practical negative charging performance.
It should also be noted that silica fine particles are added to the toner in many cases in an attempt to impart fluidity to the toner. However, the frictional charging amount of the silica itself is known to be decreased under a high humidity and to be increased under a low humidity. It follows that where silica fine particles are added to a developing agent, which is small in the change of the frictional charging depending on the change in environment, in an attempt to impart fluidity to the developing agent, the frictional charging amount of the toner tends to be decreased under a high humidity and to be increased under a low humidity.